Active landing gear damper

ABSTRACT

An active landing gear damping system and method for decelerating a vehicle during a terrain impact event, such as an aircraft landing or crash. The system monitors aircraft state data and terrain information to predict an impact of the vehicle with the terrain. The system can then determine a target damper force for each landing gear of the vehicle and a predicted damper velocity at the time of impact. Each landing gear can include an adjustable damper valve, wherein adjustment of the damper valves varies the damping coefficient of the respective dampers. The system can adjust valves of the respective dampers to provide the target force based on the predicted damper velocity. After an impact begins, the system can continuously monitor and adjust the valve to maintain the target force.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of co-pending U.S. patent applicationSer. No. 14/188,589, filed Feb. 24, 2014 and entitled “ACTIVE LANDINGGEAR DAMPER”, which is herein incorporated by reference in its entirety.

FEDERALLY-SPONSORED RESEARCH OR DEVELOPMENT

This invention was made with Government support under Contract NumberW911W6-10-2-0003 awarded by the Department of Defense. The Governmenthas certain rights in this invention.

BACKGROUND

In aircraft impact situations (e.g., landings or crashes), an aircraft'slanding gear can absorb some energy of the impact. In crash situations,the landing gear can impact terrain first and slow down the airframebefore the airframe subsequently impacts the terrain. Specifically, eachlanding gear can include a damper that resists rapid compression of thelanding gear. This resistance can decelerate the airframe during animpact.

Current landing gear damping systems are passive and are designed toprovide optimal deceleration in a crash impact for a specific aircraftgross weight and for a specific crash velocity. However, no two crashesare identical. Over the course of a flight, an aircraft's weight willdecrease as it burns fuel and/or releases weapons/cargo. Also, indifferent circumstances, aircraft will impact terrain 106, at differentvelocities and/or attitudes. As a result, the aircraft's landing gearmay not provide the optimum energy absorption capability to absorb thekinetic energy of the aircraft in a crash.

SUMMARY

Embodiments of a damper for a vehicle suspension system can include acontinuously adjustable damper valve. Adjustment of the damper valve canchange a damping coefficient of the damper. The damper can also includea motor that adjusts the damper valve. The damper can also include acontroller. The controller can receive a target damper force and aninitial damper velocity for an impact of the vehicle with terrain. Inresponse to the received target damper force and initial dampervelocity, the controller can operate the motor to adjust the dampervalve to a position corresponding to a damping coefficient that resultsin the target damper force at the initial damper velocity. After animpact begins, the controller can operate the motor to reduce anydifference between the target damper force and the actual damping forceof the damper.

Embodiments of an aircraft can include avionics and/or computers thatdetermine aircraft state data. The aircraft can also include a terraindatabase (e.g., a digital map) comprising terrain information. Theaircraft can include a plurality of landing gear. Each landing gear caninclude an adjustable damper that provides a damping force that opposesmotion of a portion of the landing gear relative to an airframe of theaircraft. Each adjustable damper can include a continuously adjustabledamper valve. Adjustment of the damper valve can change a dampingcoefficient of the damper. Each damper can also include a motor thatoperates to adjust the damper valve. The aircraft can also include acontroller. The controller can calculate, based on the aircraft statedata and terrain information, target damper forces and initial dampervelocities for each damper for an impact of the aircraft with terrain.The controller can then operate the motors of the dampers to adjust therespective damper valves to positions corresponding to dampingcoefficients that result in the target damper forces at the initialdamper velocities. After an impact begins, the controller can operateeach motor to reduce differences between the target damper forces andthe actual damping forces of the respective dampers.

Embodiments of methods for damping an impact of a vehicle with terraininclude predicting impact parameters of the vehicle. The vehicle caninclude terrain supports (e.g., landing gear, skids, floats, skis, andwheels), wherein each terrain support is coupled to the vehicle by asuspension component and wherein each suspension component includes anadjustable damper. Each adjustable damper can be adjusted to change adamping coefficient of the damper. Based on the predicted impactparameters, the method can include determining a target damper force anda predicted initial impact damper velocity for each damper. The methodcan that include adjusting each adjustable damper to achieve therespective target damper forces based on the respective initial impactvelocities. After the impact has begun, the method can include adjustingthe adjustable dampers to reduce differences between respective actualdamping forces and the respective target damping forces.

BRIEF DESCRIPTION OF THE SEVERAL DRAWINGS

FIG. 1A illustrates an exemplary scenario in which a helicopter crashesinto terrain;

FIG. 1B illustrates an exemplary scenario in which a fixed-wing aircraftcrashes into terrain;

FIG. 2 illustrates an exemplary trailing-link type of landing gear;

FIG. 3A illustrates a cross-sectional view of an exemplary damper in anextended position;

FIG. 3B is a cross-sectional view of the damper of FIG. 3A moving towarda contracted position;

FIG. 4A is a cross-sectional view of an embodiment of an active landinggear damper in an extended position;

FIG. 4B is a cross-sectional view of the active landing gear damper ofFIG. 4A in a contract position;

FIG. 4C is a cross-sectional view of a channel housing of the activelanding gear damper of FIG. 4A, wherein a valve arranged in a channel isin a fully open position;

FIG. 4D is the cross-sectional view of the channel housing of FIG. 4C,wherein the valve arranged in the channel is in a partially openposition;

FIG. 4E is the cross-sectional view of the channel housing of FIG. 4C,wherein the valve arranged in the channel is in a fully closed position;

FIG. 5A is a graph illustrating exemplary landing gear load factors fordifferent aircraft weights and at different impact velocities;

FIG. 5B is a graph illustrating exemplary landing gear damper targetforces for different aircraft weights and at different impactvelocities;

FIG. 6A is a block diagram illustrating components of a system forcontrolling an active landing gear damper and data used by the system;

FIG. 6B illustrates an exemplary helicopter in an exemplary environment,wherein various aircraft data used by the system of FIG. 6A is depicted;

FIG. 6C illustrates the exemplary helicopter with additional aircraftdata used by the system of FIG. 6A depicted;

FIG. 6D illustrates the exemplary helicopter of FIG. 6C with aircraftpitch information used by the system of FIG. 6A depicted;

FIG. 6E illustrates the exemplary helicopter of FIG. 6C with aircraftroll information used by the system of FIG. 6A depicted;

FIG. 6F illustrates the exemplary helicopter of FIG. 6C with aircraftyaw information used by the system of FIG. 6A depicted;

FIG. 6G illustrates the exemplary helicopter of FIG. 6C impactingterrain in a nose-high attitude;

FIG. 6H illustrates the exemplary helicopter of FIG. 6C impactingterrain in a rolled attitude;

FIG. 6I illustrates the exemplary helicopter of FIG. 6C impacting slopedterrain;

FIG. 6J illustrates the exemplary helicopter of FIG. 6C impacting slopedterrain; and

FIG. 7 illustrates a method for adjusting an adjustable damper for animpact.

DETAILED DESCRIPTION

As described above, in aircraft impact events such as landings and crashevents, an aircraft's landing gear can absorb some or all of the impactenergy. Specifically, referring to FIG. 1A, in a crash event 100, thelanding gear 104 of an aircraft 102 can absorb some kinetic energy 108of the aircraft 102 when the aircraft 102 impacts terrain 106. FIG. 1Aillustrates a helicopter (i.e., an aircraft 102) before and afterimpacting terrain 106. Upon impact, the landing gear 104 can compressand/or collapse, thereby absorbing some energy of the crash to minimizethe amount of energy to be absorbed by the remainder of the aircraftsystem. FIG. 1B illustrates a fixed-wing aircraft 112 before and afterimpacting the terrain 106. The landing gear 114 of the fixed wingaircraft 112 can absorb some kinetic energy 118 of the aircraft 112before the remainder of the aircraft 112 impacts terrain 106.

Passive landing gear systems are designed to provide optimaldeceleration during a crash for a specific aircraft gross weight and fora specific crash velocity. However, no two crashes are identical. Overthe course of a flight, an aircraft's weight will decrease as it burnsfuel and/or releases weapons/cargo. Also, in different circumstances,aircraft will impact terrain 106, at different velocities and/orattitudes. As a result, the landing gear of an aircraft may not providethe optimal energy absorption capability to absorb the kinetic energy108 of the aircraft. Embodiments of landing gear described hereinincorporate an adjustable damper that can vary a damping rate of landinggear to account for variations in aircraft weight, attitude, and impactvelocity, among other factors, to maximize the energy absorption of thelanding gear.

Referring now to FIG. 2, an exemplary aircraft landing gear structure200 is shown. The landing gear structure 200 depicted is a trailing linklanding gear arrangement. The trailing link landing gear includes afirst link 204 that can be connected to and/or coupled to the aircraftframe 202 of an aircraft. A second link 206 can be connected to and/orcoupled to the first link 204 by a pivot 208. The second link 206 cantrail behind the first link 204 (as indicated by arrow 203 thatillustrates the forward direction of the aircraft). An aircraft tire 210(shown in hidden lines) can be connected to a distal end of the secondlink 206 via an axle 212. When the aircraft tire 210 impacts terrain106, the tire 210 and axle 212 can move toward the aircraft frame 202 asthe second link 206 rotates about the pivot 208. A damper 214 can bearranged between and connected to the second link 206 and the aircraftframe 202. The damper 214 can provide a damping force that resistsrelative movement between the second link 206 and the aircraft frame202. The damper 214 can be connected to the aircraft frame 202 by afirst pivot joint 220 and is connected to the second link 206 by asecond pivot joint 222. The first pivot joint 220 and second pivot joint222 enable the damper 214 to pivot relative to the aircraft frame 202and the second link 206.

Landing gear configurations other than trailing link landing gear canalso incorporate embodiments of dampers described below. Furthermore,landing gear that incorporate dampers described below do not necessarilyrequire wheels. For example, landing gear incorporating dampersdescribed below can use skids, skis, and/or floats in place of wheels.

Referring now to FIGS. 3A and 3B, a damper 300 resists motion byrestricting flow of a fluid out of a first volume 314. FIG. 3A shows adamper 300 in a fully extended position wherein the upper mount 310 andthe lower mount 312 are separated by a distance D1. FIG. 3B shows thedamper 300 in a fully compressed position where the upper mount 310 andthe lower mount 312 are separated by a smaller distance D2. The damper300 can include a cylinder 302 with a piston 306 arranged therein. Ashaft 304 can be attached to the piston 306. One mount 310 can beconnected to the shaft 304 and the other mount 312 can be connected tothe cylinder 302. The cylinder 302 and the piston 306 can define a firstvolume 314 and a second volume. The piston 306 can include at least oneopening 308 through which fluid in the first volume 314 can pass to thesecond volume 316. FIGS. 3A and 3B illustrate the opening 308 as a gapbetween walls of the cylinder 302 and an outer diameter of the piston306. However, the opening 308 can also be an aperture or apertures inthe piston 306 or a passage leading out of the first volume 314 (e.g.,to an exterior reservoir). As the piston 306 moves downward from theposition shown in FIG. 3A to the position shown in FIG. 3B, fluid canflow through the opening 308 from the first volume 314 (as indicated byarrows 318) to the second volume 316. The opening 308 providesresistance to the flow of the fluid. The smaller the opening 308 is, themore resistance there is to the flow of the fluid out of the firstvolume 314. The amount of force F required to move the piston 306downwardly is proportional to the square of the velocity with which thepiston 306 moves. Put differently, more force F is required to move thepiston 306 at a fast velocity v than at a slow velocity. The forcerequired to move an ideal piston is given by the equation:

F=c·v ²;  (1)

where F is the force required, v is the velocity at which the piston ismoving relative to the cylinder, and c is a damping coefficient. Thedamping coefficient c is a function of a viscosity of the fluid and alsothe size of the opening(s) 308. The damping coefficient c increases asthe fluid gets more viscous. Also, the damping coefficient c increasesas the opening(s) 308 decrease in size (i.e., become more restrictive tothe fluid flowing there through).

In FIGS. 3A and 3B, the lower mount 312 is shown to be stationary suchthat only the upper mount 310 is moving. In a landing gear systemhowever, both the upper mount 310 and the lower mount 312 can be moving.Referring again to FIG. 2, when the landing gear structure 200 contactsthe terrain 106, the lower pivot joint 222 of the damper 214 can movedownwardly toward the terrain 106 as the second link 206 rotates aboutpivot 208. The lower pivot joint 222 of the damper 214 can also movedownwardly if the aircraft tire 210 compresses upon impact with theterrain and/or if the tire 210 sinks into the terrain 106 (e.g., if theterrain 106 is sand or marsh). In such instances where both the uppermount 310 in the lower mount 312 can be moving, again, it is therelative velocity between the upper mount 310 and lower mount 312 thatdetermines the resulting damping force F.

Referring now to FIGS. 4A-4E, embodiments of an adjustable damper 400can include an adjustable valve 420 that varies the size of arestriction for damping fluid escaping a volume 411. Referring primarilyto FIGS. 4A and 4B, embodiments of the damper 402 can include a cylinder406 and a shaft 404. The shaft 404 can includes a first mount 410arranged thereon, and the cylinder 406 can include a second mount 412mounted thereon. The shaft 404 can be connected to a piston 408 arrangedin the cylinder 406. The piston 408 and cylinder 406 can define a volume411 filled with fluid (e.g. damping fluid). In various embodiments, thecylinder can be arranged on a housing 419. The housing 419 can define aninlet channel 416 and an outlet channel 418. The inlet channel 416 canbe in communication with the volume 411 via an opening 414. Similarly,the outlet channel 418 can be in communication with a reservoir via anopening 425. The valve 420 can be arranged between the inlet channel 416and the outlet channel 418. Referring now to FIGS. 4C-4E, the valve 420can include walls 423 that define a channel 421 therebetween. Thechannel 421 in the valve 420 can be in communication with the inletchannel 416 and the outlet channel 418. Furthermore, the valve 420 isrotatable within the housing 419 to vary the amount of communicationbetween the channel 421 of the valve and the inlet channel 416 and/orthe outlet channel 418. FIG. 4C illustrates the valve 420 in its fullyopen position such that dampening fluid flow (depicted by arrow 434) canflow from the volume 411 through the inlet channel 416 to the outletchannel 418. FIG. 4D illustrates the valve 420 rotated to a partiallyopen position in which the dampening fluid can still flow through thevalve 420, but is restricted more than in FIG. 4C. FIG. 4E illustratesthe valve 420 in a fully closed position wherein no fluid flow passesthrough the valve 420.

As the valve 420 moves from the fully-open position shown in FIG. 4C tothe fully-closed position shown in FIG. 4E, the damping coefficient cfor the adjustable damper increases. As the valve 420 reaches thefully-closed position, the damping coefficient c can approach infinity.The minimum damping coefficient c when the valve is in the fully-openposition shown in FIG. 4C) can depend on the arrangement of the valve420 relative to the volume 411. For example, referring to FIGS. 4A and4B, the opening 414 to the inlet channel 416, the inlet channel 416, theoutlet channel 418, and the valve 420 can each apply a restriction orresistance to flow of damping fluid from the volume 411, resulting in aminimum damping coefficient c when the valve is in the fully-openposition shown in FIG. 4C. A look-up table of damping coefficient cvalues for different valve positions can be prepared through operationof an adjustable damper 400 at different valve 420 positions.

Referring again to FIGS. 4A and 4B, the valve 420 can be connected to afirst end of a shaft 422. A second end of the shaft 422 can be connectedto an output of a gearbox 424. The gearbox 424 can be driven by a motor426 (e.g., a continuously adjustable electric, hydraulic, or pneumaticservo motor). The motor 426 can be continuously adjustable such that itcan be driven to any particular rotational position (e.g., number ofturns or fractions of turns). The gearbox 424 can multiply the torqueprovided by the motor 426, thereby allowing a smaller motor to be used.Furthermore, the gearbox 424 can protect the motor 426 from being backdriven by the valve 420 (i.e., fluid passing through the valve 420 mayexert a force on the valve 420 that would cause the valve 420 to turntoward a more open or more closed position). The gearbox 424 can provideresistance to the valve 420 being turned that the flowing fluid cannotovercome.

The motor 426 can also be connected to an encoder 428 that can track andreport a rotational position (e.g., a number of turns of the motor froma starting position) of the motor 426. The motor 426 and encoder 428 canbe connected to a damper controller 430 via a communication line 432. Incertain embodiments, the damper controller 430 can be integral with theencoder 428. In such embodiments, each damper 402 can include a dampercontroller 430. In various other embodiments, a central dampercontroller 430 can communicate with and control the encoders 428 andmotors 426 of each damper 402 of respective landing gear for anaircraft. The damper controller 430 can translate the reportedrotational position of the motor into a rotational position of thevalve.

Referring now to FIGS. 5A and 5B, a particular aircraft can have anoptimal landing gear load factor g (i.e., deceleration or “g” force) forits landing gear for a given impact velocity. FIG. 5A illustrates anexemplary graph 500 showing optimal load factors for landing gear asimpact velocity increases for an aircraft at different weights W₁, W₂,and W₃ (wherein W₂ is heavier than W₁ and W₃ is heavier than W₂). Thelanding gear load factor g is an amount of deceleration (in multiples ofgravity g) that the landing gear imparts on the aircraft when theaircraft impacts the ground at a particular velocity. The load factor(g) is derived from the equation:

F=m·g;  (2)

where F equals the force being exerted on the aircraft by the landinggear (e.g., by the landing gear damper), m equals the portion of mass ofthe aircraft on the landing gear, and g is the acceleration (i.e.,deceleration) of the aircraft. Equation (2) can be reorganized as:

$\begin{matrix}{g = {\frac{F}{m}.}} & (3)\end{matrix}$

The exemplary graph 500 shows that a minimum landing gear load factor gmay be optimal at relatively low impact velocities. For example, at lowimpact velocities (e.g., impact velocities experienced during a normallanding), a landing gear load factor g of two times gravity (i.e., 2g's) may be sufficient to prevent the landing gear from fullycompressing. Similarly, there can be a maximum landing gear load factorg for the landing gear. For example, the landing gear mounts (thelocations where the landing gear is attached to the airframe) may breakif subjected to loads above six g's. Thus, the load (for that particularlanding gear) should not exceed six g's.

FIG. 5A also shows that, at a particular impact velocity, the landinggear load factor g decreases as an aircraft gets heavier. For example,at a given impact velocity, a medium weight W₂ aircraft (depicted bycurve 510) will have a lower landing gear load factor than a lightweight W₁ aircraft (depicted by curve 508). Similarly, at a given impactvelocity, a heavy weight W₃ aircraft (depicted by curve 512) will have alower landing gear load factor g than the medium weight W₂ aircraft orthe light weight W₁ aircraft. The landing gear load factor g decreasesas weight increases for a given impact velocity because the damper forceat the given impact velocity is the same but must decelerate a heavieraircraft.

Referring now to FIG. 5B, to provide the same load factor g to anaircraft at any weight for an impact at a given speed, the force F beingexerted on the aircraft by the landing gear must be increased as theaircraft weight increases. The graph 520 of FIG. 5B shows that themedium weight W₂ aircraft (depicted by curve 544) has a higher targetdamper force than the light weight W₁ aircraft (depicted by curve 546).Similarly, the heavy weight W₃ aircraft (depicted by curve 542) has ahigher target damper force than the medium weight W₂ aircraft or thelight weight W₁ aircraft. Referring again to equation (1), the targetdamper force F at a given velocity can be changed by varying the dampingcoefficient c. Referring again to FIGS. 4A-4E, by measuring the dampingcoefficient c for the adjustable damper 400 resulting from differentpositions of the valve 420, a model of damping coefficients c fordifferent positions of the valve 420 can be provided. For example, thedamper controller 430 can include a lookup table that provides dampingcoefficients c for different positions of the valve 420.

Referring now to FIGS. 6A-6J, embodiments of a damping system canevaluate various aircraft data to predict an impact velocity for eachlanding gear of an aircraft and predict how much of the aircraft'sweight will be supported by each landing gear. FIG. 6A is a blockdiagram of an exemplary damping system 600 that can receive at least oneof various aircraft state data 602 and terrain information from aterrain database 604. The aircraft state data 602 (described in greaterdetail below) can be provided by various avionics and/or computers inthe aircraft that can communicate with the damping system 600.Similarly, the terrain database 604 can be stored in avionics and/orcomputers in the aircraft that can communicate with the damping system600.

An impact prediction module 606 of the damping system 600 can receivethe aircraft state data 602 and terrain data from the terrain database604 to predict the characteristics of an impending crash and to outputto a damper controller 616 at least one of a target damper force 614 anda predicted initial damper velocity 615. The target damper force 614corresponds to a damper force calculated to result in the desired landgear load factor g based on the portion of aircraft weight applied to aparticular landing gear. The damper controller 616 uses the targetdamper force 614 and initial damper velocity 615 to set an initial valveposition of the valve 420. After an impact has started, the dampercontroller 616 can continuously adjust the position of the valve 420 toachieve the desired damper force F. As an impact progresses and theaircraft decelerates, the damper velocity will slow. As a result, thedamper force F and landing gear load factor g will decrease unless thevalve 420 is rotated to a more closed position (thereby increasing thedamping coefficient c). During an impact event, the damper controller616 (and specifically the feedback module 620) can operate the motor 426to rotate the valve to increase the damping coefficient c to maintainthe damping force F at the target damper force 614. The target damperforce 614 can also be transferred to a damper force difference module622 within the feedback module 620. The damper force difference module622 can compare the received target damper force 614 for a damper withthe actual damper force being generated by the damper.

Referring again to the aircraft state data 602, the damping system 600can receive various information about the operation of the aircraft fromaircraft sensors, avionics, and/or computers. FIGS. 6B-6F depict variousaircraft state data that can be received by the damping system 600. Forexample, referring to FIG. 6D, various sensors and/or avionics on anaircraft 632 (e.g. helicopter) can provide information about at leastone of the pitch, pitch rate, and pitch acceleration 636 of theaircraft. Referring to FIG. 6E, various sensors and/or avionics on theaircraft can provide information about at least one of the role, rollrate, and roll acceleration 638 of the aircraft. Referring to FIG. 6F,various sensors and/or avionics on the aircraft can provide informationabout at least one of the yaw, yaw rate, and yaw acceleration 640 of theaircraft. The pitch 636, roll 638, and/or yaw 640 information can beused to determine the aircraft's current attitude, and to predict itsattitude, at some future time (e.g., a future time that corresponds witha predicted impact).

Referring to FIG. 6B, the aircraft's current position can be determinedfrom a global positioning satellite (GPS) receiver 644 and/or from aninertial navigation system (INS). The aircraft's current position canalso be determined from other navigation systems, such as Long RangeNavigation (LORAN) systems, VHF Omni Directional Radio Range (VOR)navigation, and/or non-directional bearing (NDB) navigation. Theaircraft's altitude relative to the ground (e.g., altitude above groundlevel (AGL)) can be determined from a number of sources. For example,the position received by the GPS receiver 644 can include an altitudeabove sea level. The altitude above sea level can also be determinedfrom an altimeter onboard the aircraft. The aircraft position(determined above) can be used to retrieve terrain elevation informationfrom the terrain database 604 for the terrain below the aircraft. Theretrieved terrain elevation information can be subtracted from theaircraft altitude above sea level to determine the aircraft altitudeabove ground level. The aircraft's AGL can also be determined using aradar altimeter 642 on board the aircraft.

Still referring to FIG. 6B, various aircraft avionics and/or sensors candetermine at least one of the aircraft's velocity and acceleration inthree dimensions (e.g. V_(X), V_(Y), V_(Z), A_(X), A_(Y), and A_(Z))634. For example, the avionics and/or sensors can include an attitudeand heading reference system (AHRS) and/or a gyroscopic flightinstrument system to determine the aircraft velocities andaccelerations.

Referring to FIG. 6C, the aircraft state data 602 can also includeinformation about at least one of the weight 648 of the aircraft 632 aswell as the center of gravity (CG) of the aircraft 632. FIG. 6C depictsan exemplary aft CG 650 and an exemplary forward CG 650′. The weight 648of the aircraft can be calculated throughout a flight by an aircraftcomputer. The computer can start with a known empty weight of theaircraft, a known fuel load and/or munitions load of the aircraft, andan estimated passenger weight of the aircraft. As an example, anaircraft flight plan may assume that each person on board the aircraftweighs two hundred pounds. If 5 people are on board the aircraft, thenthe estimated passenger weight for the aircraft would be 1,000 pounds.As the flight progresses and fuel is burned and/or munitions aredischarged, the weight of the aircraft will decrease. The aircraftcomputer can track the amount of fuel and/or munitions used and decreasethe calculated weight as the flight progresses.

The aircraft center of gravity can also be tracked by a computer onboardan aircraft 632 (e.g., helicopter). An aircraft can have a known emptyweight center of gravity. Adding fuel, munitions, cargo, and/orpassengers can cause the center of gravity to shift forward or aftdepending on the their placement in the aircraft. Items like fuel andmunitions often have a known affect on the center of gravity becausefuel is stored in defined, unmovable tanks and weapons are oftenarranged on defined, unmovable mounting points on the aircraft.Therefore, adjustments to the center of gravity for the fuel weightand/or munitions weight can be automatically performed based on theweights alone. Similarly, as fuel and/or munitions are used, thecomputer can automatically recalculate the center of gravity by removingthe weights of the spent fuel and/or munitions. By contrast, cargoand/or passengers may be loaded into an aircraft in variousconfigurations. As a result, the computer may require a weight and aplacement location of passengers and/or cargo to calculate the center ofgravity.

In various embodiments, the aircraft may calculate the center of gravitybased on straight and level flight performance of the aircraft. Forexample, an aircraft may require more “nose down” control input for anaircraft with an aft CG 650 than an aircraft with a forward CG 650′. Theaircraft may calculate the center of gravity based on control inputsduring steady state flight and correlating the control inputs to aparticular center of gravity.

In various embodiments, the aircraft state data 602 can also includeinformation about lift being generated by the aircraft. In the exampleshown in FIG. 6C, a helicopter generates lift 646 from its spinningrotor blades. The amount of lift 646 being generated can be calculatedand/or estimated by monitoring engine power, rotor shaft load, and/orrotor torque, for example. For a fixed wing aircraft (e.g. aircraft 112shown in FIG. 1B), the amount of lift 646 being generated can becalculated and/or estimated by monitoring airspeed and angle of attack,for example.

The damping system 600 can also receive terrain information from aterrain database 604. In various embodiments, the terrain database 604can be stored onboard the aircraft in a computer storage medium, forexample. In various other embodiments, the terrain database 604 can bestored at a ground-based location and portions of the terrain database604 can be transmitted and/or uploaded to the aircraft 632. For example,portions of the terrain database 604 corresponding to the position ofthe aircraft 632 can be transmitted and stored locally in a computersystem of the aircraft 632. As another example, portions of the terraindatabase 604 that are relevant to a particular flight of the aircraft632 may be uploaded and stored locally in a computer system of theaircraft 632. The terrain database 604 can include information about atleast one of terrain elevation, slope, and surface type. The informationcan be keyed to location (e.g., latitude and longitude) such that thedamping system 600 can access terrain information proximate to thecurrent position of the aircraft.

The impact prediction module 606 of the damping system 600 can includean aircraft trajectory and attitude module 608. The aircraft trajectoryand attitude module 608 can receive the aircraft state data 602 as wellas information from the terrain database 604. The aircraft trajectoryand attitude module can use the aircraft state data 602 and terraindatabase 604 information to predict whether an impact event is imminent.For example, in various embodiments, the aircraft trajectory andattitude module can use the velocities V_(X), V_(Y), and V_(Z) tocalculate the present velocity vector of the aircraft (i.e., the currentaircraft travel direction) and can use the accelerations A_(X), A_(Y),and A_(Z) to predict changes to the current velocity vector. From thevelocity vector and accelerations, the aircraft trajectory and attitudemodule 608 of the damping system 600 can predict the trajectory 652 ofthe aircraft 632 and determine whether the aircraft will impact terrain.

In various embodiments, the damping system 600 can compare differentaircraft state data 602 and/or terrain information to determine whethera crash is imminent. For example, the helicopter depicted in FIGS. 6B-6Jmay be flying straight and level over relatively flat terrain when itflies relatively close to and over the top of a skyscraper. In such aninstance, the radar altimeter 642 may indicate a rapid decrease inaltitude above ground level (e.g., the top of the skyscraper). However,other altitude data (e.g., received from an aircraft altimeter and/or aGPS receiver 644) and terrain information from the terrain database 604may be used to contradict the radar altimeter 642 reading.

In the event that the aircraft trajectory and attitude module 608predicts an impending impact with terrain, the module 608 can outputpredicted impact parameters 610. The predicted impact parameters caninclude at least one of the aircraft impact velocity (i.e., the verticalspeed with which the aircraft will impact the terrain 654), the aircraftattitude with which the aircraft will impact the terrain 654, theaircraft gross weight at the time of impact, the aircraft's center ofgravity at the time of impact, and the terrain surface type. In variousembodiments, the predicted impact parameters can also include the lift646 being generated by the aircraft 632.

The first parameter, aircraft velocity at the time of impact, can affectthe force generated by dampers in the landing gear. In certainembodiments, the aircraft velocity can be a component of the aircraftvelocity that is perpendicular to terrain. For a wheeled aircraftimpacting level terrain, the downward component of the velocity of theaircraft can determine the magnitude of the impact energy and theinitial speed of the dampers. If the aircraft impacts upward-sloping ordownward-sloping terrain, then the forward component of the aircraft canincrease or decrease, respectively, the magnitude of the impact energyand the initial speed of the dampers.

Referring primarily to FIGS. 6G-6J, the aircraft's attitude at the timeof impact relative to the terrain 654 can affect how much load may beapplied to each landing gear of the aircraft. For example, FIG. 6Gillustrates the aircraft 632 impacting the terrain 654 with a nose upattitude. Consequently, landing gear 660 will impact the terrain beforelanding gear 662 impacts the terrain 654. As a result, landing gear 660may have a larger load applied to it than landing gear 662. As anotherexample, FIG. 6H illustrates the aircraft 632 impacting the terrain 654,in a rolled attitude. Consequently, landing gear 664 impacts the terrain654 before landing gear 666 impacts the terrain 654. As a result,landing gear 664 may have a larger load applied to it than landing gear666. The terrain 654 at the location of impact may have a slope, and theslope of the terrain 654 can contribute to uneven loading of thedifferent landing gear of the aircraft. For example, FIG. 6I illustratesthe aircraft 632 impacting the terrain 654′ in a level attitude, but theterrain 654′ is arranged at a slope with an angle of a. Consequently,the landing gear 660 may impact the terrain 654′ before landing gear 662impacts the terrain 654′. As a result, landing gear 660 may have alarger load applied to it than landing gear 662. As another example,FIG. 6J illustrates the aircraft 632 impacting the terrain 654″ in alevel attitude, but the terrain 654″ is arranged at a slope with anangle of β. Consequently, landing gear 664 may impact the terrain 654″before landing gear 666 impacts the terrain 654″. As a result, landinggear 664 may have a larger load applied to it than landing gear 666.

The calculated weight of the aircraft and center of gravity of theaircraft (discussed above) can also affect the amount of load applied toeach of the landing gear of the aircraft in an impact. As discussedabove, the landing gear dampers must provide a larger damper force to aheavy aircraft than to a light aircraft to achieve the same landing gearload factor g. The center of gravity of the aircraft can affect adistribution of the weight of the aircraft on the landing gear uponimpact with terrain 654. For example, referring primarily to FIG. 6C, ifthe aircraft 632 has an aft center of gravity 650, then landing gear 660may have a larger portion of the overall weight of the aircraft 632applied to it than landing gear 662. Conversely, if the helicopter has aforward center of gravity 650′, then landing gear 662 may have a largerportion of the overall weight of the aircraft 632 applied to it thanlanding gear 660.

The terrain surface type of the terrain 654 can also affect the damperforces applied to the aircraft during an impact. As described above, thelanding gear may at least partially sink into soft terrain surfaces suchas sand, mud, or marsh. By comparison, the landing gear may not sink atall into hard soil, rock, or asphalt (e.g., a runway). As describedabove, if the landing gear sinks into the terrain upon impact, then theinitial velocity of the dampers at the moment of impact may be slowerthan if the landing gear does not sink into the terrain. The terrainsurface type can include a factor that can be used to estimate the speedof the landing gear as it sinks into the terrain. For example, thefactor may vary between zero and one, a factor of zero can mean thatthat the surface is hard (e.g., asphalt) and the landing gear will notsink into the surface. By contrast, water may have a factor of one,meaning that the landing gear will sink into the water at the samevelocity as the remainder of the aircraft. Sand, for example, may have afactor of 0.5, meaning that at the time of impact, the landing gear willsink into the sand at a velocity that is half of the velocity of theremainder of the aircraft. The values described above are illustrativeonly. The values of the factor may depend, among other reasons, on thetype of landing gear and also the speed of impact. For example, a tireon a landing gear model may sink into snow-covered surface at adifferent rate than a landing gear equipped with a ski. Also, the amountof resistance a surface applies to the landing gear sinking in maychange with impact speed. For example, at low speeds, water may providealmost no resistance to landing gear sinking into the water surface.However, at higher speeds, the amount of resistance by water to thelanding gear can increase.

As discussed above, the impact parameters 610 can optionally include thelift 646 being generated by an aircraft at the time of impact with theterrain 654. The lift 646 can affect the loads on the landing gear (e.g.landing gear 660 and 662) upon impact. For example, the aircraft 632depicted in FIGS. 6B-6J may be generating lift 646 equal to two timesthe weight of the helicopter at the time of impact. In this example, thelift 646 is not sufficient to prevent the aircraft from impactingterrain 654. However, upon impact, the lift 646 can mitigate some of theload that would otherwise be borne by the landing gear (e.g. landinggear 660 and 662).

Referring again to FIG. 6A, the predicted impact parameters 610 can beforwarded to a landing gear modeling module 612. The landing gearmodeling module 612 can use the predicted impact parameters 610 todetermine a landing gear load factor g for each landing gear of theaircraft. Referring again to FIG. 5A, the landing gear load factor g canbe an optimal deceleration provided by a landing gear based on thepredicted impact velocity. The landing gear modeling module 612 can thencalculate a target damper force 614 for each landing gear of theaircraft based on the determined landing gear load factors g for therespective landing gear and based on the portion of the weight of theaircraft predicted to be supported by each landing gear upon impact.

The landing gear modeling module 612 can also output a predicted initialdamper velocity 615 for each landing gear. The predicted initial dampervelocity 615 is the predicted speed that the 2 ends of a landing geardamper will move towards one another at the instant of impact (e.g., seevelocity V in FIG. 3B). For a number of reasons, the predicted initialdamper velocity 615 can differ from the impact velocity of the aircraft.First, as described above, the landing gear may at least partially sinkinto the terrain 654, which may slow the initial damper velocity 615.The landing gear modeling module 612 can predict any effect on thepredicted initial damper velocity 615 from soft terrain based on theterrain surface type information received in the predicted impactparameters 610. Second, the landing gear geometry may affect thepredicted initial damper velocity 615 relative to the aircraft velocity.For example, referring to FIG. 2, when the landing gear structure 200contacts the terrain 106, the aircraft frame 202 may move downwardlytoward the axle 212 (the second link 206 and axle 212 will rotate aboutpivot 208). The damper 214, which is mounted to the aircraft frame 202via a first pivot joint 220 and to the second link 206 via a secondpivot joint 222, can compress as the aircraft frame 202 moves toward theaxle 212. However, the damper 214 will compress at a slower rate thanthe aircraft frame 202 moves toward the axle 212 because the damper 214is located inboard of the axle 212 relative to the pivot 208. Thus, inthe example shown in FIG. 2, the initial damper velocity may be lessthan the aircraft impact velocity. Any difference between the predictedaircraft impact velocity and the predicted initial damper velocity 615due to geometry differences will be landing gear design specific and canbe preprogrammed into the landing gear modeling module.

Referring again to FIG. 6A, at least one of the target damper force 614and predicted initial damper velocity 615 can be transmitted to a dampercontroller 616. As explained above, in various embodiments, each landinggear damper can include a separate damper controller 616. In suchembodiments, the impact prediction module 606 can send a separate targetdamper force 614 to each damper controller 616. In various otherembodiments, a central damper controller 616 can control the damper ofeach landing gear. In such embodiments, the impact prediction module 606can send a damper target force signal that includes target damper forceis 614 for each landing gear damper.

In the damper controller 616, at least one of the target damper force614 and predicted initial damper velocity 615 can be used to calculatean initial valve position 618. Referring to equation (1) above, for eachdamper, the damping coefficient c can be determined based on thepredicted initial damper velocity 615 that will result in the targetdamper force 614. The damper controller 616 can then use a lookup tableor the like to determine a position of the valve (e.g., valve 420) thatcorresponds to the desired damping coefficient c. The damper controller616 can then drive the motor 426 of each damper until the encoder 428reports that the valve (e.g., valve 420) is properly positioned.

The impact prediction module 606 can also output the target damper force614 to a feedback module 620 inside the damper controller 616. After thelanding gear impacts the terrain 654, the feedback module of the dampercontroller 616 can control the motor 426 to vary the valve position tomaintain the target damper force 614 as the landing gear compresses. Thefeedback module 620 can include a damper force sensor 624. The damperforce sensor 624 may be a strain gauge and/or a load cell that directlymeasures force. Alternatively, the damper force sensor 624 can derivethe damper force. For example, the damper force sensor 624 can be alinear encoder that measures the position of the damper piston relativeto the cylinder. By measuring the position of the damper piston atregular time intervals, a piston velocity can be calculated. Then,knowing the valve 420 position and the calculated piston velocityenables a calculation of damper force. The feedback module 620 comparesthe actual damper force (measured by damper force sensor 624) to thetarget damper force 614 (at the damper force difference module 622) andcomputes a new valve position (see block 626) to reduce the errorbetween the target damper force 614 and the actual damper force(measured by damper force sensor 624). In various embodiments, thefeedback module 620 may be a proportional-integral-derivative (PID)controller.

In addition to minimizing any errors between the target damper force 614and actual damper force (measured by damper force sensor 624), thefeedback module 620 can also adjust the damper valve (e.g., valve 420)position (by operating the motor 426) to maintain the target damperforce 614 as the damper velocity slows down. Referring again to FIGS. 5Aand 5B, as the relative velocity of the damper ends toward one anotherdecreases, the force generated by the damper also decreases. Thefeedback module 620 can adjust the valve to a more restrictive position.As a result, the damping coefficient c can be increased such that theactual damper force (measured by damper force sensor 624) remainsapproximately the same.

Referring now to FIG. 7, a method 700 for damping an aircraft impactwith terrain is shown. In block 702, a system can predict the locationof an impact with terrain and also determine at least one of the impactvelocity and the aircraft attitude at the time of the impact. The systemcan also predict at least one of the weight of the aircraft and thecenter of gravity of the aircraft at the time of impact. Also, using theterrain database, the system can determine the type of terrain theaircraft will impact (e.g., prepared surface, soil, and water). Thetypes of terrain can include additional types (e.g., asphalt, dirt,sand, marsh, etc.).

In block 704, the system can set a target damper force for each landinggear of the aircraft based on the above parameters that will result inan optimal landing gear load factor G for each landing gear. At leastone of the target damper force and a predicted initial damper velocitycan be transmitted to a damper controller.

In block 706, the damper controller can receive at least one of thetarget damper force and predicted initial damper velocity and calculatea damping coefficient c, required to achieve the target damper forcebased on the initial damper velocity. The damper controller can use alookup table or the like, to determine an initial valve position thatcorresponds to the calculated damping coefficient c.

Referring now to block 708, after impact, the damper controller cancontinuously measure the actual damper force (e.g., via a load cell,strain gauge, or the like) and compare the actual damper force to thetarget damper force. In various embodiments, the damper controller cancontinuously measure the actual damper force. The controller can adjustthe valve position to minimize the error between the actual damper forceand the target damper force. In various embodiments, the controller cancontinuously adjust the valve position. The controller can also adjustthe valve position to increase the damping coefficient c as the aircraftand the damper decelerate during the impact. In various embodiments, thecontroller continues to operate for as long as possible after an impactevent begins. For example, a crash event may sever communication betweenthe controller and the remainder of aircraft systems such that thecontroller may not be able to determine that a crash event has ended.

In various other embodiments, in block 710, the system checks to see ifthe impact event is complete. If not, then the method 700 returns toblock 708 and continues to adjust the valve position to maintain thetarget force. The controller may determine whether an impact event iscomplete in a number of ways. For example, as described above, as animpact event progresses and the damper decelerates, the valve of thedamper will be moved to the closed position to maintain the targetdamping force. In various embodiments, the controller can determine thatthe impact event is completed once the valve is fully closed. In variousother embodiments, the controller may determine that an impact event iscompleted after the detected force (e.g., force detected by the forcesensor) has not changed in a threshold time period (e.g., five seconds).If the controller determines that an impact event has ended, then themethod 700 moves to block 712 and ends.

The systems and methods disclosed herein are not limited to aircraft.For example, various embodiments of the systems and methods can beapplied to any vehicle suspension, such as automobiles, motorcycles,tanks, and trucks. For example, tanks can drive quickly over unimprovedsurfaces and can sometimes “jump” over bumps in the terrain. Variousembodiments of the above-described system can be used to adjust thedamping profile of the suspension of the tank when the tank lands aftera “jump.”

Embodiments of the system can also be used in non-impact situations. Forexample, helicopters can be susceptible to a hazardous known as groundresonance in which a vibration in the rotor can match a natural resonantfrequency of the airframe in contact with the ground. Ground resonancecan destroy a helicopter in a matter of seconds. Adjusting theadjustable dampers of the system may change the natural resonantfrequency of the airframe and stop a ground resonance situation beforethe vibration amplifies and damages the helicopter.

The descriptions of the various embodiments have been presented forpurposes of illustration, but are not intended to be exhaustive orlimited to the embodiments disclosed. Many modifications and variationswill be apparent to those of ordinary skill in the art without departingfrom the scope and spirit of the described embodiments.

Aspects of the present embodiments may be embodied as a system, methodor computer program product. Accordingly, aspects of the presentdisclosure may take the form of an entirely hardware embodiment, anentirely software embodiment (including firmware, resident software,micro-code, etc.) or an embodiment combining software and hardwareaspects that may all generally be referred to herein as a “circuit,”“module” or “system.” Furthermore, aspects of the present disclosure maytake the form of a computer program product embodied in one or morecomputer readable medium(s) having computer readable program codeembodied thereon.

Any combination of one or more computer readable medium(s) may beutilized. The computer readable medium may be a computer readable signalmedium or a computer readable storage medium. A computer readablestorage medium may be, for example, but not limited to, an electronic,magnetic, optical, electromagnetic, infrared, or semiconductor system,apparatus, or device, or any suitable combination of the foregoing. Morespecific examples (a non-exhaustive list) of the computer readablestorage medium would include the following: an electrical connectionhaving one or more wires, a portable computer diskette, a hard disk, arandom access memory (RAM), a read-only memory (ROM), an erasableprogrammable read-only memory (EPROM or Flash memory), an optical fiber,a portable compact disc read-only memory (CD-ROM), an optical storagedevice, a magnetic storage device, or any suitable combination of theforegoing. In the context of this document, a computer readable storagemedium may be any tangible medium that can contain, or store a programfor use by or in connection with an instruction execution system,apparatus, or device.

A computer readable signal medium may include a propagated data signalwith computer readable program code embodied therein, for example, inbaseband or as part of a carrier wave. Such a propagated signal may takeany of a variety of forms, including, but not limited to,electro-magnetic, optical, or any suitable combination thereof. Acomputer readable signal medium may be any computer readable medium thatis not a computer readable storage medium and that can communicate,propagate, or transport a program for use by or in connection with aninstruction execution system, apparatus, or device.

Computer program code for carrying out operations for aspects of thepresent disclosure may be written in any combination of one or moreprogramming languages, including an object oriented programming languagesuch as Java, Smalltalk, C++ or the like and conventional proceduralprogramming languages, such as the “C” programming language or similarprogramming languages. The program code may execute entirely on theuser's computer, partly on the user's computer, as a stand-alonesoftware package, partly on the user's computer and partly on a remotecomputer or entirely on the remote computer or server. In the latterscenario, the remote computer may be connected to the user's computerthrough any type of network, including a local area network (LAN) or awide area network (WAN), or the connection may be made to an externalcomputer (for example, through the Internet using an Internet ServiceProvider).

Aspects of the present disclosure are described above with reference toflowchart illustrations and/or block diagrams of methods, apparatus(systems) and computer program products according to embodiments of thedisclosure. It will be understood that each block of the flowchartillustrations and/or block diagrams, and combinations of blocks in theflowchart illustrations and/or block diagrams, can be implemented bycomputer program instructions. These computer program instructions maybe provided to a processor of a general purpose computer, specialpurpose computer, or other programmable data processing apparatus toproduce a machine, such that the instructions, which execute via theprocessor of the computer or other programmable data processingapparatus, create means for implementing the functions/acts specified inthe flowchart and/or block diagram block or blocks.

These computer program instructions may also be stored in anon-transitory computer readable medium (including any of the mediatypes described above), for example, that can direct a computer, otherprogrammable data processing apparatus, or other devices to function ina particular manner, such that the instructions stored in the computerreadable medium produce an article of manufacture including instructionswhich implement the function/act specified in the flowchart and/or blockdiagram block or blocks.

The computer program instructions may also be loaded onto a computer,other programmable data processing apparatus, or other devices to causea series of operational steps to be performed on the computer, otherprogrammable apparatus or other devices to produce a computerimplemented process such that the instructions which execute on thecomputer or other programmable apparatus provide processes forimplementing the functions/acts specified in the flowchart and/or blockdiagram block or blocks.

The flowchart and block diagrams in the Figures illustrate thearchitecture, functionality, and operation of possible implementationsof systems, methods and computer program products according to variousembodiments of the present disclosure. In this regard, each block in theflowchart or block diagrams may represent a module, segment, or portionof code, which comprises one or more executable instructions forimplementing the specified logical function(s). It should also be notedthat, in some alternative implementations, the functions noted in theblock may occur out of the order noted in the figures. For example, twoblocks shown in succession may, in fact, be executed substantiallyconcurrently, or the blocks may sometimes be executed in the reverseorder, depending upon the functionality involved. It will also be notedthat each block of the block diagrams and/or flowchart illustration, andcombinations of blocks in the block diagrams and/or flowchartillustration, can be implemented by special purpose hardware-basedsystems that perform the specified functions or acts, or combinations ofspecial purpose hardware and computer instructions.

While the preceding is directed to embodiments of the presentdisclosure, other and further embodiments of the disclosure may bedevised without departing from the basic scope thereof, and the scopethereof is determined by the claims that follow.

What is claimed is:
 1. An aircraft, comprising: avionics configured todetermine aircraft state data; a terrain database comprising terraininformation; a plurality of landing gear, wherein each landing gearcomprises an adjustable damper configured to provide a damping forcethat opposes motion of a portion of the landing gear relative to anairframe of the aircraft, wherein each adjustable damper comprises: anadjustable damper valve, wherein adjustment of the damper valve changesa damping coefficient of the damper; and a motor, wherein operation ofthe motor adjusts the damper valve; and a controller configured to:calculate, based on at least the determined aircraft state data and theterrain information, predicted impact parameters; calculate, based onthe predicted impact parameters, a target damper force and predictedimpact velocity for each damper; operate the motor of each damper toadjust the respective damper valves to positions corresponding todamping coefficients that result in the respective target damper forcesat the respective initial damper velocities; and thereafter, operate themotor of each damper to reduce any difference between actual dampingforces and target damping forces of respective dampers.
 2. The aircraftof claim 1, wherein the predicted impact parameters based on at leastthe determined aircraft state data and the terrain information includeat least one of: a terrain surface type, an aircraft impact velocity, animpact attitude relative to the terrain at time of impact, an aircraftgross weight at time of impact, and an aircraft center of gravity attime of impact, wherein the controller calculates the target damperforce based on a target landing gear load factor and the predictedimpact parameters, and wherein the impact prediction module calculatesthe initial damper velocity based on the predicted impact parameters. 3.The aircraft of claim 1, wherein the aircraft state data comprises atleast one of: pitch, pitch rate, and pitch acceleration data; roll, rollrate, and roll acceleration data; yaw, yaw rate, and yaw accelerationdata; a three-dimensional velocity vector; a three-dimensionalacceleration vector; a position; an altitude above ground level; anaircraft weight; and an aircraft center of gravity.
 4. The aircraft ofclaim 1, wherein the terrain information comprises at least one of:terrain elevation; terrain slope; and terrain surface type.
 5. Theaircraft of claim 1, wherein the motor of each of the plurality oflanding gear comprises a continuously adjustable servomotor.
 6. Theaircraft of claim 1, further comprising a gearbox arranged between themotor and the adjustable valve of the damper of each landing gear,wherein the gearbox is configured to multiply torque from the motor andapply the multiplied torque to the adjustable valve.